Transcript [insert project name here]

Advanced Robotics – 49274
“Wobble”
Milestone Presentation
Patrick Barnes - 01057280
Jin Sub Lee - 10198885
Arild Hjelle - 10115588
Spring 2004
Project Goals
• To design, build, and test a 2-wheeled
balancing robot.
• To demonstrate the capabilities of the robot
as a simple autonomous platform.
Background
• Based on inverted pendulum
– Classic control problem
– Well understood
• Commercial products exist
– Segway
– iBot 3000
• Many prototypes exist...
Stages
Stage 1
Balance upright using a potentiometer and
‘whisker’ to detect relative ground orientation.
Stage 2
Balance using inertial measurement (gyroscope,
accelerometer) - without any auxiliary ground
contact.
Stage 3
Navigate using high-level directives - ‘left’,
‘right’, ‘forward’, ‘backwards’, ‘stop’.
Basic Hardware
• Actuators
– Differential drive
• 2 motors - left & right
• Full mobility
• Zero turning circle
• Sensors
– Wheel encoders
• Used for dead reckoning
• Needed for balance
– Pitch sensor
• Either ‘whisker’ or
inertial measurement
System Diagram
Batteries
(4.8Ah 14.4V)
Legend:
0/1
Status
LEDS
(Ground lines not shown for clarity)
Low voltage
warning
5V
reg
ulat
or
Atmel 90S8535
Gyro
ADXL
Dual
Motor
Controller
(PWM control)
enc
od
er
M
Left
14.4V Power
5V Power
Control signals
Sensor inputs
Motor Control
enc
od
Right er
M
Input/Output formats:
Low voltage warning:
Logic 1 when battery low.
Gyroscope:
~50Hz pulse width modulation
1ms - 2ms duty cycle
ADXL202JQC (Accelerometer)
2-channel analogue signal
PWM can also be used
Duty cycle corresponds to g's
Wheel Encoders (Quadrature)
Minimal processing done
At each pulse, gives direction
Status LEDs
Indicate internal state of uC
May be a 7-segment display
Motor Controller
2-channel PWM control
PWM amplitude x2
Direction signal x2
Power supply
Motors
• Motors
– RS 550 S
– 14.4V
– Sourced from a cheap cordless drill
• Controller
–
–
–
–
Dual H-bridge controller - L298N
PWM control
3A Capacity
Stackable
‘Whisker’
• Low-friction potentiometer
• Attached to wire whisker
• Senses angle w.r.t. ground - NOT gravity.
Inverted Pendulum
• Limited range of movement
• Direct (physical) measurement of pitch
angle and rate
+ wheels
• Unlimited range of movement
• Indirect (inertial) measurement of pitch
angle and rate
Theory
• Balancing:
– Open-loop control system
– Speed and pitch angle are an indirect result of
motor speeds
• Steering
– Closed-loop control system
– Heading is a direct result of relative motor
speeds
De-coupling control systems
• Balancing
– If an equal torque offset is applied to both
wheels, the heading is unaffected
• Steering
– If an equal but opposite torque offset is applied
to the left and right wheels, pitch and speed are
unaffected*
• Balance and Steering can be considered
separately
Six State Space Variables
• xRM
• vRM
• θP
• ωP
•δ
• δ˙
straight line position [m]
straight line speed [m/s]
pitch angle [rad]
pitch rate [rad/s]
yaw angle [rad]
yaw rate [rad/s]